Seismometers such as this one installed near Mount
Spurr volcano (on skyline in background) provide the Alaska
Volcano Observatory with a continuous, radio-telemetered
record of volcanic earthquakes. These data are used to
monitor the state of activity at the volcano and are
critical to the ability of the Observatory to issue timely
warnings of eruptions. View is to the north. Photograph by
C. Neal , U.S. Geological Survey, June 3, 1993.